A nerve or plexus block is achieved through the administration of variable quantities of an anesthetic agent to a nerve or nerve plexus. Because nerves and nerve plexuses are very fragile structures, not capable of simple repair or reconstruction, it is important to do as little damage as possible in locating the point at which the nerve or plexus may be contacted. Peripheral electrical nerve stimulation is one method that has been proposed for locating medical needles and catheters proximate to nerves and nerve plexuses.
An embodiment of a prior-art peripheral electrical nerve stimulation system 50 for locating and placing needles and catheters proximate to a nerve or plexus is illustrated in FIGS. 5A and 5B. A system similar to system 50 is illustrated and described in U.S. Pat. No. 6,973,346 to Fred Hafer et al., the contents of which are incorporated herein by reference.
System 50 includes a needle assembly 52, a catheter assembly 54, and a nerve stimulator 56. Needle assembly 52 comprises a metal, electrically conductive needle 52A, an insulating coating 52B, and a hub 52C. Needle 52A comprises a proximal end 52E, a distal end 52D, and a hollow, cylindrical cavity 52F that extends the length of needle 52A.
Catheter assembly 54 comprises a catheter 54A, a catheter adapter 54B, and an electrical contact 54C. Catheter 54A is sized so as to be able to be disposed within needle 52A, specifically within cavity 52F of needle 52A, through hub 52C. Catheter 54A comprises a catheter sheath 54G having a proximal end 54E and a distal end 54D. Spanning an interior cavity of catheter sheath 54G extending the entire length of catheter 54A from proximal end 54E to distal end 54D is a coiled wire 54F. Coiled wire 54F is in electrical communication with electrical contact 54C. Catheter sheath 54G is nonconductive and insulates coiled wire 54F along the length of catheter 54A except at distal end 54D where a portion of coiled wire 54F is exposed.
Nerve stimulator 56 attaches to needle assembly 52 through an alligator clamp 58. More specifically, alligator clamp 58 clamps directly to needle 52A to provide an electrical connection from nerve simulator 56 to needle 52A. Nerve stimulator 56 also attaches to catheter assembly 54 through alligator clamp 58. More specifically, alligator clamp 58 clamps to electrical contact 54C to provide an electrical connection from nerve stimulator 56 to coiled wire 54F.
During the administration of a plexus block using system 50, nerve stimulator 56 is clamped to needle assembly 52 using alligator clamp 58. Needle 52A is inserted into a patient and an electrical current provided by nerve stimulator 56 is applied to needle 52A. Insulating coating 52B on needle 52A causes the electrical current conducted by needle 52A to pass through to the portion of needle 52A exposed at distal end 52D. A contraction of a particular observed muscle indicates the proximity of distal end 52D of needle 52A to a plexus of interest in the patient. After the desired plexus is located, alligator clamp 58 is removed from needle 52A and attached to electrical contact 54C of catheter assembly 54.
Catheter 54A is then fed through hub 52C of needle assembly 52, through interior cavity 52F of needle 52A, and out past distal end 52D of needle 52A to a desired position. As with needle 52A, because catheter sheath 54G is nonconductive, current passes through catheter 54A to the patient through the portion of coiled wire 54F exposed at distal end 54D. Again, a contraction of the particular observed muscle indicates the proximity of distal end 54D of catheter 54A to the plexus of interest in the patient. Needle 52A may then be removed, and catheter 54A may be securely fixed. Alligator clamp 58 is then disconnected and anesthetic agents are administered through catheter 54A to the nerve plexus.